Subsurface structures are installed to perform various environmental, geotechnical, and petroleum recovery functions. In the case of environmental and geotechnical applications, containment walls and treatment barriers are typically installed to extend from the ground surface to a subsurface zone. In these applications, the containment walls may include flow containment walls which contain the flow of underground liquids, and treatment barriers which are permeable zones filled with reactive material. In many cases, the construction process must penetrate many feet below the ground surface before reaching a subsurface zone that requires a structure such as a containment wall or a treatment barrier. Examples of construction techniques performed in the prior art are sheet piling walls, slurry walls, braced excavations, and continuous trenches.
Current construction techniques required to install the above containment walls and treatment barriers share many common problems, such as the necessity to reroute underground utilities, potential structural damage to existing buildings and structures, potentially large staging areas for construction equipment, specialized and expensive equipment. In many cases, the removal and proper disposal of contaminated soils and liquids recovered from the excavation is required. Most of the above examples, for either economical or technical reasons, have a maximum wall or barrier depth that may not allow a project to be completed or even begun.
Turning now to the prior art, hydraulic fracturing of subsurface earth formations to stimulate production of hydrocarbon fluids from subterranean formations has been carried out in many parts of the world for over fifty years. The earth is hydraulically fractured either through perforations in a cased well bore or in an isolated section of an open bore hole. The horizontal and vertical orientation of the hydraulic fracture is controlled by the compressive stress regime in the earth and the fabric of the formation. It is well known in the art of rock mechanics that a fracture will occur in a plane perpendicular to the direction of the minimum stress, see U.S. Pat. No. 4,271,696 to Wood. At significant depth, one of the horizontal stresses is generally at a minimum, resulting in a vertical fracture formed by the hydraulic fracturing process. It is also well known in the art that the azimuth of the vertical fracture is controlled by the orientation of the minimum horizontal stress.
At shallow depths, the horizontal stresses could be less or greater than the vertical overburden stress. If the horizontal stresses are less than the vertical overburden stress, then vertical fractures will be produced; whereas if the horizontal stresses are greater than the vertical overburden stress, then a horizontal fracture will be formed by the hydraulic fracturing process.
Techniques to induce a preferred horizontal orientation of the fracture from a well bore are well known. These techniques include slotting, by either a gaseous or fluid jet under pressure, to form a horizontal notch in an open bore hole. Such techniques are commonly used in the petroleum and environmental industry. The slotting technique performs satisfactorily in producing a horizontal fracture, provided that the horizontal stresses are greater than the vertical overburden stress, or the earth formation has sufficient horizontal layering or fabric to ensure that the fracture continues propagating in the horizontal plane. Perforations in a horizontal plane to induce a horizontal fracture from a cased well bore have been disclosed, but such perforations do not preferentially induce horizontal fractures in formations of low horizontal stress. See U.S. Pat. No. 5,002,431 to Heymans.
Various means for creating vertical slots in a cased well bore have been disclosed. The prior art recognizes that a chain saw can be used for slotting the casing. See U.S. Pat. No. 1,789,993 to Switzer; U.S. Pat. No. 2,178,554 to Bowie, et al., U.S. Pat. No. 3,225,828 to Wisenbaker; and U.S. Pat. No. 4,119,151 to Smith. Installing pre-slotted or weakened casing has also been disclosed in the prior art as an alternative to perforating the casing. See U.S. Pat. No. 5,103,911 to Heijnen. These methods in the prior art were not concerned with the azimuth orientation of two opposing slots for the preferential initiating of a vertical hydraulic fracture at a predetermined azimuth orientation. It has been generally accepted in the art that the fracture azimuth orientation cannot be controlled by such means. These methods were an alternative to perforating the casing to achieve better connection between the well bore and the surrounding formation.
In the art of hydraulic fracturing subsurface earth formations from subterranean wells at depth, it is well known that the earth's compressive stresses at the region of fluid injection into the formation will typically result in the creation of a vertical two "winged" structure. This "winged" structure generally extends laterally from the well bore in opposite directions and in a plane generally normal to the minimum in situ horizontal compressive stress. This type of fracture is well known in the petroleum industry as that which occurs when a pressurized fracture fluid, usually a mixture of water and a gelling agent together with certain proppant material, is injected into the formation from a well bore which is either cased or uncased. Such fractures extend radially as well as vertically until the fracture encounters a zone or layer of earth material which is at a higher compressive stress or is significantly strong to inhibit further fracture propagation without increased injection pressure.
It is also well known in the prior art that the azimuth of the vertical hydraulic fracture is controlled by the stress regime with the azimuth of the vertical hydraulic fracture being perpendicular to the minimum horizontal stress direction. Attempts to initiate and propagate a vertical hydraulic fracture at a preferred azimuth orientation have not been successful, and it is widely believed that the azimuth of a vertical hydraulic fracture can only be varied by changes in the earth's stress regime. Such alteration of the earth's local stress regime has been observed in petroleum reservoirs subject to significant injection pressure and during the withdrawal of fluids resulting in local azimuth changes of vertical hydraulic fractures.
The determination of the hydraulic fracture geometry, such as its horizontal or vertical orientation, azimuth and length of the vertical fracture, and the extent and depth of a horizontal fracture, can be made from the measurement of earth tilts by conventional surface or bore hole mounted biaxial tiltmeters, see U.S. Pat. No. 4,271,696 to Wood. Highly sensitive electronic tiltmeters, capable of measuring tilts less than 10.sup.-7 radians, measure the earth's deformation due to the opening and propagation of a hydraulic fracture. From monitoring these tilts in real time along with the flow of injected fluid, the hydraulic fracture geometry can be determined. See U.S. Pat. Nos. 4,271,696 and 4,353,244 to Wood. Influence functions that relate the opening of a fracture to ground deformation can be utilized to calculate the fracture geometry. As suggested by U.S. Pat. No. 5,002,431 to Heymans, the fracture geometry can be determined and controlled from the measurement of tilts and real time computer control. Heymans does not detail how the fracture geometry may be determined, nor does Heymans disclose how the interaction of ground tilts from multiple fractures can be resolved to determine fracture geometry.
The method of determining the hydraulic fracture geometry, disclosed by U.S. Pat. No. 4,353,244 to Wood, has a number of deficiencies. If (a) the fracture is non-planar, (b) if the fracture is not of the full initiated height, or (c) if multiple fractures are initiated in close proximity of each other, then fracture geometry determination is not assured.
Accordingly, there is a need for a method and apparatus for controlling the azimuth orientation of a vertical hydraulic fracture in formations of unconsolidated or weakly cemented sediments and soils.
There is a further need for a method and apparatus for monitoring and calculating in real time the propagation of the azimuth of vertical hydraulic fractures.
And, there is a further need for a method and apparatus for the creation and control of coalesced, overlapping, and interconnecting fractures to form a treatment barrier or containment wall formed from a fracture fluid.